1. Field of the Invention
The present invention relates generally to a device for visually indicating a current location of a vehicle. More particularly, the invention relates to an improved apparatus for determining and visually indicating a current location of an automotive vehicle to the driver thereof, wherein a stable and quick-start locating operation is attained from the combination of an earth magnetism sensor and a rate type gyroscope by the selection of one of the two which suits the particular situation at hand.
2. Description of Relevant Art
A known apparatus has been developed for the determination and visual indication of a current location of an automotive vehicle to the driver thereof, which comprises a travel distance counter section adapted to determine the current mileage or travel distance of an automotive vehicle in terms of, for example, its travel speed, and a bearing detector section adapted to detect the current orientation and extent of azimuthal deviation of the vehicle in accordance with its travel direction per a given distance from its starting point. The current location of the vehicle along its travel route is obtained arithmetically from the thus-obtained detection data, the result of which calculation is visually indicated on a display for the driver of the vehicle by way of spot information varying from time to time upon a suitable road map shown on the display indicating the travel route along which the vehicle is currently travelling.
In the aforesaid known apparatus for visually indicating a current location of an automotive vehicle, there is employed a rate type gyroscope or the like adapted to detect a possible angular velocity produced about the axis of yawing motion of the vehicle, so as to detect a current relative relationship such as, for example, a current angular relationship between the orientation of a current horizontal component of the earth magnetism and a current travel direction of the vehicle.
In such a bearing detecting apparatus which employs a rate type gyroscope, errors are likely to be accumulated during the bearing detecting operation as developed from possible drifts of the gyroscope during vehicle operation to such an extent that information obtained from the thus-accumulated errors presents an erroneous location indication of the vehicle on the display screen, despite the fact that such a system is advantageously inherently immune from disturbances such as earth magnetism as experienced when an earth magnetism sensor is employed for the bearing detection of the automotive vehicle.
Also known to those skilled in the art is a bearing detecting apparatus of an earth magnetism sensor type which presents by way of the earth magnetism a current relative relationship between the current horizontal component of the earth magnetism and the current orientation of the vehicle with a relatively reliable operation on the average over a long distance, because it can consistently present the absolute orientation of the vehicle with respect to the current location thereof, unlike the apparatus employing the rate type gyroscope. In contrast, however, from a short-term standpoint, such an apparatus of the earth magnetism sensor type is inconveniently substantially susceptible to external disturbances such as from a railroad crossing or an iron bridge as the vehicle passes thereby, or such as when a large-sized truck travels near to the vehicle, so that the display at the driver's seat presents undesired incorrect information on a current location of the vehicle which would very possibly deviate from a predetermined course of travel due to thus-far accumulated errors in the location detecting operation.
When the vehicle is under the foregoing conditions, it is very difficult or even impossible for the driver of the vehicle to determine whether the displayed information on the screen is incorrect or if his vehicle is actually travelling in a different or incorrect way, thus resulting in substantial ambiguity.
The present invention effectively overcomes the aforesaid inconveniences and difficulties experienced with the conventional location detecting apparatus for use in an automotive vehicle.